Wireless repeater using a single RF chain for use in a TDD wireless network

ABSTRACT

A repeater for re-transmitting an incoming RF signal comprising: a first antenna array for receiving the incoming RF signal; a second antenna array for transmitting an outgoing RF signal; and a transceiver for down-converting the incoming RF signal to a down-converted signal, processing the down-converted signal, and up-converting the processed signal to produce the outgoing RF signal. The first antenna array is cross-polarized with respect to the second antenna array. The repeater also comprises an echo processor for attenuating in the down-converted signal an echo signal associated with the outgoing RF signal. The echo processor delays transmission of the outgoing RF signal in order to minimize the echo signal.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

The present invention is related to that disclosed in U.S. ProvisionalPatent Application Ser. No. 60/608,299, filed Sep. 7, 2004, entitled“Method and Procedure for Using a Single RF Chain in a Wireless RepeaterFor Time-Division Duplexed Signals” and U.S. Provisional PatentApplication Ser. No. 60/608,282, filed Sep. 7, 2004, entitled “Methodand Procedure for Reduction of Feedback in a Wireless Repeater UsingCancellation of Cross-Polarized Signals”. U.S. Provisional PatentApplication Ser. Nos. 60/608,282 and 60/608,299 are assigned to theassignee of the present application. The subject matter disclosed ineach of U.S. Provisional Patent Application Ser. Nos. 60/608,282 and60/608,299 is hereby incorporated by reference into the presentdisclosure as if fully set forth herein. The present invention herebyclaims priority under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication Ser. Nos. 60/608,282 and 60/608,299.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to communication networks and,more specifically, to a wireless network repeater that uses a single RFchain to repeat signals in a time-division duplexed (TDD) wirelessnetwork.

BACKGROUND OF THE INVENTION

Consumers use a wide range of devices and networks, including cellularphones, paging devices, personal communication services (PCS) systems,and wireless data networks. Wireless service providers create newmarkets for wireless devices and expand existing markets by makingwireless devices and services cheaper and more reliable. Wirelessservice providers attract new customers by reducing infrastructure costsand operating costs, by increasing handset battery life, and improvingquality of service, and new and better features.

Inadequate coverage is a persistent problem in the quality of service ofany wireless network. Natural and man-made obstacles frequently createradio frequency (RF) “holes” in the coverage area of a wireless network.Voice and data call connections are frequently dropped when a wirelessterminal, such as a cell phone or a similar mobile station, enters an RFhole. Mobile stations that are already in an RF hole may not be able toreliably establish new connections. Typical areas in which RF holesoccur include underground tunnels, buildings that have large footprints,tall buildings, and underground shopping malls.

Wireless service providers may attempt to improve coverage by deployingRF repeater transceivers. A variety of repeaters have been developed toimprove the coverage of wireless networks. In U.S. patent applicationSer. No. 09/998,238 (Publication No. 20030104781), Son describes aresidential wireless repeater that achieves isolation between transmitand receive antennas by physical separation of the antennas. Therepeater disclosed by Son requires two separate modular repeaters thatcommunicate simultaneously with each other with low radio frequency.

In U.S. Pat. No. 6,731,904, Judd describes a modular repeater thatincludes a housing having a pair of substantially 180° oppositely facingsurfaces. At least one antenna element is mounted to each of thesesurfaces for radiating energy in a direction opposite that of anotherantenna element mounted to the other surface. An electronic circuitwithin the housing operatively couples signals between at least oneantenna element on each of the oppositely facing surfaces of the modulehousing.

In U.S. Pat. No. 6,697,603, Lovinggood et al. describe a digitalrepeater for receiving and retransmitting radio frequency (RF) signals.The Lovinggood repeater down-converts a received RF signal to anintermediate frequency (IF) signal, converts the IF signal into adigital signal, processes and amplifies the digital signal into anamplified signal using the digital signal processor, and converts theamplified signal into an analog signal. The Lovinggood repeater thenup-converts the analog signal to an outgoing RF signal suitable forantenna transmission.

In U.S. Pat. No. 6,640,112, Lee et al. describe a repeating method for awireless communication system which provides time and space diversities.The method of repeating a forward link communication signal for awireless communication system includes the steps of: a) transmitting theforward link communication signal through a first transmitting antenna;b) delaying the forward link communication signal for a predeterminedtime period; and c) transmitting a delayed forward link communicationsignal which is generated by step b) through a second transmittingantenna.

In U.S. Pat. No. 4,283,795, Steinberger presents an adaptivecross-polarization cancellation arrangement in which a first desiredpolarized signal and a second interfering orthogonally polarized signal,including cross-polarization components, are concurrently received at anantenna. The orthogonally polarized components of the received signalare separated and transmitted along separate paths and recombined afterthe phase and amplitude of the separated polarized interfering signalsample have been adjusted for maxim cancellation of cross-polarizationcomponents in the other path.

Each of the prior art repeaters described above requires at least one ofthe following: i) physical separation of primary and secondary antennasets by a significant distance to reduce the magnitude of the transferfunction H such that H<1/G, where G is the repeater power gain; ii)precise adjustment of input-output phase adjustment embodied in H suchthat the vector product G*H is <0 in order to yield negative feedback;iii) separate modules for the reception of external signals and theretransmission of signals internal to the building; and iv) methods forthe cancellation of multiple time-delayed echoes that would occur in ahome or in-building environment with multiple scattering surfaces. Theprior art repeaters generally do not provide a method of canceling anyechoes from the output that would lead to unstable operation (i.e.,oscillations).

Therefore, there is a need in the art for improved repeaters for use inwireless networks. In particular, there is a need for a repeater thatcancels echoes and avoids oscillation.

SUMMARY OF THE INVENTION

The present invention provides a wireless repeater having a single radiofrequency (RF) chain for use in a time-division duplexed (TDD)IEEE-802.16 (or similar) wireless network. A repeater according to theprinciples of the present invention reduces the feedback between anoutput antenna and an input antenna that could cause instabilities (oroscillations) in the repeater. The present invention uses a combinationof antenna cross-polarization techniques and digital processingtechniques to remove time-delayed feedback or echo terms. Thiscombination of techniques greatly reduces the feedback between a donorantenna and a server antenna. Isolation factors may exceed 20 dB foroppositely-directed, cross-polarized antennas. The signal processingtechniques described herein may provide another 20-40 dB of gainisolation.

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention to provide a repeater forre-transmitting an incoming RF signal. According to an advantageousembodiment of the present invention, the repeater comprises: 1) a firstantenna array for receiving the incoming RF signal; 2) a second antennaarray for transmitting an outgoing RF signal; and 3) a transceiver chaincapable of down-converting the incoming RF signal to a down-convertedsignal, processing the down-converted signal, and up-converting theprocessed signal to thereby produce the outgoing RF signal. The firstantenna array comprises a first antenna element and the second antennaarray comprises a second antenna element that is cross-polarized withrespect to the first antenna element.

According to one embodiment of the present invention, a ground planeassociated with the repeater is disposed between the first antenna arrayand the second antenna array to thereby provide isolation between thefirst and second antenna arrays.

According to another embodiment of the present invention, thetransceiver chain further comprises an echo processor capable ofattenuating in the down-converted signal an echo signal associated withthe outgoing RF signal.

According to still another embodiment of the present invention, the echoprocessor delays transmission of the outgoing RF signal in order tominimize the echo signal in the down-converted signal.

According to yet another embodiment of the present invention, the echoprocessor comprises an echo detector for detecting the echo signal inthe down-converted signal.

According to a further embodiment of the present invention, the echoprocessor further comprises an echo suppressor for suppressing at leasta part of the echo signal from the down-converted signal.

According to a still further embodiment of the present invention, theecho processor comprises a time delay buffer for delaying transmissionof the outgoing RF signal.

According to a yet further embodiment of the present invention, the echoprocessor further comprises a test signal generator capable of adding aknown test signal to the outgoing RF signal.

In one embodiment of the present invention, the echo processor iscapable of detecting an echo of the test signal in the down-convertedsignal and using a delay associated with the test signal echo todetermine a delay associated with the delay buffer.

In another embodiment of the present invention, the repeater furthercomprises a switching circuit capable of coupling the first antennaarray to an input of the transceiver chain and the second antenna to anoutput of the transceiver chain in a first switch position and furthercapable of coupling the second antenna array to an input of thetransceiver chain and the first antenna to an output of the transceiverchain in a second switch position.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an exemplary wireless network in which a repeateraccording to the principles of the present invention may be implemented;

FIG. 2 illustrates an exemplary repeater according to one embodiment ofthe present invention;

FIG. 3 is an architectural view of the exemplary repeater according toone embodiment of the present invention;

FIG. 4 illustrates an exemplary signal processor block according to oneembodiment of the present invention;

FIG. 5 illustrates an exemplary echo processor block according to oneembodiment of the present invention; and

FIG. 6 illustrates an exemplary echo processor block according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 6, discussed below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any suitably arranged RF repeater transceiver.

FIG. 1 illustrates exemplary wireless network 100, which implementsrepeater 120 according to the principles of the present invention.Wireless network 100 comprises base station (BS) 101 and other basestations (not shown) that communicate with a plurality of mobilestations, such as mobile station (MS) 111, located in a coverage area ofwireless network 100. In an advantageous embodiment of the presentinvention, base station (BS) 101 communicates with mobile station (MS)111 over time-division duplexed (TDD) channels. The TDD channels may usecode division multiple access (CDMA) signals or orthogonal frequencydivision multiple access (OFDMA) signals. MS 111 may be any suitablewireless device, including a conventional cellular radiotelephone, a PCShandset device, a personal digital assistant (PDA), a portable computer,a telemetry device, or the like, that is capable of communicating withBS 101 via wireless links.

The present invention is not limited to mobile devices. Other types ofwireless access terminals, including fixed wireless terminals, may beused. For the sake of simplicity, only mobile stations are shown anddiscussed hereafter. However, it should be understood that the use ofthe term “mobile station” in the claims and in the description below isintended to encompass the exemplary types of mobile stations describedabove, as well as portable devices such as, for example, vehicle-mountedwireless devices.

Wireless network 100 further comprises wireless repeater 120. Forwardchannel (i.e., downlink) signals from BS 101 to MS 111 and reversechannel (i.e., uplink) signals from MS 111 to BS 101 may be blocked byobjects 131-134. Repeater 120 may be used in wireless network 100 toextend the coverage range of BS 101 to areas, such as the vicinity of MS111, where blockage or scattering causes large propagation losses.Objects 131-134 may include, for example, tunnels, terrain features(e.g., mountains, valleys), and large buildings.

Repeater 120 comprises donor antenna array 122, which communicates inthe forward and reverse channels with BS 101, and server antenna array124, which communicates in the forward and reverse channels with MS 111.Repeater 120 is placed in a location where the forward channel signalreceived from BS 101 exceeds a specified threshold. Repeater 120 filtersand amplifies the received signal and retransmits the signal into theregions where the signal from BS 101 is too low for reliable reception.Repeater 120 performs a similar function in the reverse channel from MS111 to BS 101.

FIG. 2 illustrates exemplary repeater 120 according to one embodiment ofthe present invention. Repeater 120 comprises a single receive andtransmit path (i.e., a single radio frequency (RF) chain). Repeater 120comprises bandpass filter 210, low-noise amplifier (LNA) 220, signalprocessor 230, high-power amplifier (HPA) 240, bandpass filter 250, andswitch 260. Repeater 120 can repeat (i.e., re-transmit) signal in theforward channel and in the reverse channel, depending on the setting ofswitch (or duplexer) 260.

When switch 260 is in a first position, donor antenna array 122 isconnected to the input of bandpass filter 210 and server antenna array124 is connected to the output of bandpass filter 250, such thatrepeater 120 receives and retransmits forward channel signals. Whenswitch 260 is in a second position, donor antenna array 122 is connectedto the output of bandpass filter 250 and server antenna array 124 isconnected to the input of bandpass filter 210, such that repeater 120receives and retransmits reverse channel signals.

During TDD operation, donor antenna array 122 and server antenna array124 support the same transmit and receive frequencies. Switch 260 iscontrolled by the CONTROL signal and provides isolation between thetransmitter output and receiver input for the transmit and receive timeslots. For each of the transmit and receive time slots, repeater 120performs the following functions. Initially, repeater 120 receives theincoming RF modulated signal in time-slot T_(d) with a first one of theantennas (e.g., donor antenna array 122 in this example). BPF 210isolates the frequencies of interest and LNA 220 amplifies the receivedRF signal.

Next, signal processor 230 removes signal components coupled from theoutput antenna (i.e., server antenna array 124) to the input antenna(i.e., donor antenna array 122). Next, HPA 240 amplifies the regeneratedsignal. BPF 250 filters the amplified signal and the filtered amplifiedsignal is radiated from the other antenna (i.e., server antenna array124) in a translated time slot T_(d)′.

In one position of switch 260, signal flow is from server antenna array124 to donor antenna array 122 (i.e., reverse or uplink channel). In theother position of switch 260, the signal flow is from donor antennaarray 122 to server antenna array 124 (i.e., forward or downlinkchannel). Repeater 120 activates the CONTROL signal to change theduplexer switch position based on timing derived from air interfacetiming, such as pilot synchronization.

Because repeater 120 receives and transmits on the same frequency in TDDformat, it is possible for feedback to occur due to amplified,time-delayed signals coupled between the output antenna and the inputantenna. According to the principles of the present invention, repeater120 incorporates a number of techniques to minimize feedback.

FIG. 3 is an architectural view of exemplary repeater 120 according toone embodiment of the present invention. Repeater 120 uses ground planeisolation and cross-polarization of antenna elements to minimizefeedback between the donor antenna and the server antenna. Repeater 120uses orthogonally polarized antenna elements 301 and 302 on oppositefaces of the housing of repeater 120 to radiate power in directionsopposite to each other. Thus, antenna element 301 in antenna array 122is aligned at right angles with antenna element 302 in antenna array124.

Electronic circuits mounted within the housing of repeater 120 couplesignals between antenna elements 301 and 302 on the oppositely facingsurfaces. Circuits that receive low-power signals are isolated from thepower amplifier circuits for the down-link and the up-link by shieldingtechniques well-known in the field. Ground plane 330, which containsfiltered feed-through lines, provides additional isolation between theduplexer that controls the connectivity between down-conversioncircuitry 310 and up-conversion circuitry 320. This architecture alsoreduces the length of antenna feeds, a major source of coupling betweenco-located antennas.

FIG. 4 illustrates exemplary signal processor 230 according to oneembodiment of the present invention. Signal processor 230 providesfurther isolation by detecting and attenuating signals coupled from thetransmitter antenna to the receiver antenna for both the forward(downlink) channel and the reverse (uplink) channel. Signal processor230 comprises down-conversion mixer 405, analog-to-digital converter(ADC) 410, echo processor 415, digital-to-analog converter (DAC) 420,up-conversion mixer 425, local oscillator (LO) 430, clock 435 and localoscillator (LO) 440.

The incoming RF signal from LNA 220 is down-converted to baseband (orIF) by down-conversion mixer 405 and LO 430. ADC 410 converts the outputof mixer 405 to digital samples, which are stored in memory in echoprocessor 415. Echo processor 415 then removes feedback (i.e., echoes)from the digital samples. The filtered samples are converted back to ananalog signal by DAC 420 mixer 425 and LO 440 then up-convert the outputof DAC 420 to an RF signal that is fed to the input of HPA 240.

In alternate embodiments, the ADC sampling may be performed in the RFband of the received signal or at an intermediate frequency (IF) level.The samples are taken over a time interval that represents the maximumpropagation time expected for the latest arriving echo, generally lessthan 1 microsecond, for an in-building or home environment. To reducethe throughput of sampled date (bits/sec), sub-Nyquist sampling rates ineither the RF band or in the IF band may be used. ADC 410 has a dynamicrange and sampling frequency to differentiate the original, non-delayedsignal from the amplified, delayed echo. Clock 435 synchronizes ADC 410with the data transfer between blocks.

FIG. 5 illustrates exemplary echo processor 415 according to oneembodiment of the present invention. Echo processor 415 comprises echodetector 505, echo suppressor 510, delay buffer 515, controller 520,memory 525 and clock 530. Echo detector 505 searches for anytime-delayed echoes in the sampled data. Echo suppressor 510 subtractsany detected echoes from the sampled data stream. In order to reduce thecorrelation between the original signal and echoed signals, theresulting signal samples are delayed in delay buffer 515 for a timespecified by controller 520. Those familiar with the art will recognizethat conventional auto-correlation methods may be used to determine thetime delay of each echo. The echo detection and echo subtraction mayoccur serially or in multiple parallel branches, one for each expectedecho.

FIG. 6 illustrates exemplary echo processor 415 according to anotherembodiment of the present invention. In the embodiment shown in FIG. 6,repeater 120 processes orthogonal frequency division multiplexing (OFDM)signals. Echo processor 415 comprises OFDM Fast Fourier Transform (FFT)detector 605, echo suppressor 610, OFDM Inverse Fast Fourier Transform(IFFT) channel element 615, delay buffer 620, test code generator 625,controller 630, memory 635 and clock 640.

ODM IFFT channel element 615 receives a low-power OFDM/OFDMA test codegenerated by test code generator 625. This low-power test code signal issufficiently strong so that its echo may be picked up by the receiveantenna after transmission. However, the test code signal remains tooweak to cause interference to mobile stations. Since repeater 120 knowsthe exact value of the test code signal, it is relatively easy to detectthe echo of the test code signal. OFDM FFT detector 605 uses correlationor matched filter techniques in the FFT domain to detect anytime-delayed, cross-polarized text code signals coupled into the sampledsignal from the receiver input antenna. Detector 605 uses the time-delayinformation associated with the test code signal to determine the exactpropagation delay through repeater 120. Echo suppressor 610 uses thepropagation delay information to subtract each echo signal from thesampled data stored in memory 635.

To prevent the onset of instabilities or oscillations upon power up ofrepeater 120, controller 630 ramps up the output power amplifier gainwhile echo processor 415 learns of the existence of echo terms. Theamplifier gain is increased until either the maximum allowed value isreached or until echo processor 415 no longer provides sufficientsuppression of echo signals.

Repeater 120 uses a novel combination of techniques to minimize echoesin the transmitted signals. These techniques include the use oforthogonally polarized antenna elements 301 and 302 in the donor andserver sides of repeater 120, coupled with intervening signal processor230 that removes or greatly attenuates echoes coupled into the oppositepolarization. The antennas are oriented at 180-degrees with respect totheir high-gain directions, respectively. Antenna arrays 122 and 124also have high front-to-rear isolation. The echo detection andcancellation processes in signal processor 230 are greatly enhanced bythe use of delay buffers 515 and 620 that follow suppression of detectedecho components in the input signal.

Although the present invention has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present invention encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. A repeater for re-transmitting an incoming RF signal comprising: afirst antenna array for receiving said incoming RF signal; a secondantenna array for transmitting an outgoing RF signal; and a transceiverchain capable of down-converting said incoming RF signal to adown-converted signal, processing said down-converted signal, andup-converting said processed signal to thereby produce said outgoing RFsignal, wherein said first antenna array comprises a first antennaelement and said second antenna array comprises a second antenna elementthat is cross-polarized with respect to said first antenna element,wherein said transceiver chain further comprises an echo processorcapable of attenuating in said down-converted signal an echo signalassociated with said outgoing RF signal, and wherein said echo processorcomprises a delay buffer configured to delay transmission of saidoutgoing RF signal for a period of time, the time period based on theecho signal and determined by detecting a time-delayed, cross-polarizedtest code signal using at least one of correlation and matched filtertechniques in the FFT domain, the test code signal being a known testcode signal.
 2. The repeater as set forth in claim 1, wherein a groundplane associated with said repeater is disposed between said firstantenna array and said second antenna array to thereby provide isolationbetween said first and second antenna arrays.
 3. The repeater as setforth in claim 1, wherein said echo processor comprises an echo detectorfor detecting said echo signal in said down-converted signal.
 4. Therepeater as set forth in claim 3, wherein said echo processor furthercomprises an echo suppressor for suppressing at least a part of saidecho signal from said down-converted signal.
 5. The repeater as setforth in claim 4, wherein said echo processor further comprises a testsignal generator capable of adding the known test signal to saidoutgoing RF signal.
 6. The repeater as set forth in claim 5, whereinsaid echo processor is capable of detecting an echo of said test signalin said down-converted signal and using a delay associated with saidtest signal echo to determine a delay associated with said delay buffer.7. The repeater as set forth in claim 6, further comprising a switchingcircuit capable of coupling said first antenna array to an input of saidtransceiver chain and said second antenna array to an output of saidtransceiver chain in a first switch position and further capable ofcoupling said second antenna array to an input of said transceiver chainand said first antenna to an output of said transceiver chain in asecond switch position.
 8. A wireless network comprising: a plurality ofbase stations capable of communicating with a plurality of mobilestations in a coverage area of said wireless network; and a repeatercapable of re-transmitting forward channel signals from a first basestation to a first mobile station and re-transmitting reverse channelsignals from said first mobile station to said first base station, saidrepeater comprising: a first antenna array for receiving an incoming RFsignal; a second antenna array for transmitting an outgoing RF signal;and a transceiver chain capable of down-converting said incoming RFsignal to a down-converted signal, processing said down-convertedsignal, and up-converting said processed signal to thereby produce saidoutgoing RF signal, wherein said first antenna array comprises a firstantenna element and said second antenna array comprises a second antennaelement that is cross-polarized with respect to said first antennaelement, wherein said transceiver chain further comprises an echoprocessor capable of attenuating in said down-converted signal an echosignal associated with said outgoing RF signal, and wherein said echoprocessor comprises a delay buffer configured to delay transmission ofsaid outgoing RF signal for a period of time, the time period based onthe echo signal and determined by detecting a time-delayed,cross-polarized test code signal using at least one of correlation andmatched filter techniques in the FFT domain, the test code signal beinga known test code signal.
 9. The wireless network as set forth in claim8, wherein a ground plane associated with said repeater is disposedbetween said first antenna array and said second antenna array tothereby provide isolation between said first and second antenna arrays.10. The wireless network as set forth in claim 8, wherein said echoprocessor comprises an echo detector for detecting said echo signal insaid down-converted signal.
 11. The wireless network as set forth inclaim 10, wherein said echo processor further comprises an echosuppressor for suppressing at least a part of said echo signal from saiddown-converted signal.
 12. The wireless network as set forth in claim11, wherein said echo processor further comprises a test signalgenerator capable of adding the known test signal to said outgoing RFsignal.
 13. The wireless network as set forth in claim 12, wherein saidecho processor is capable of detecting an echo of said test signal insaid down-converted signal and using a delay associated with said testsignal echo to determine a delay associated with said delay buffer. 14.The wireless network as set forth in claim 13, further comprising aswitching circuit capable of coupling said first antenna array to aninput of said transceiver chain and said second antenna array to anoutput of said transceiver chain in a first switch position and furthercapable of coupling said second antenna array to an input of saidtransceiver chain and said first antenna to an output of saidtransceiver chain in a second switch position.
 15. A method forre-transmitting an incoming RF signal comprising: receiving the incomingRF signal at a first antenna array, the first antenna array having afirst antenna element; down-converting the incoming RF signal to adown-converted signal; attenuating in the down-converted signal an echosignal associated with an outgoing RF signal; up-converting theattenuated signal to thereby produce the outgoing RF signal; andtransmitting the outgoing RF signal at a second antenna array, thesecond antenna array having a second antenna element that iscross-polarized with respect to the first antenna element, wherein theattenuating step comprises delaying transmission of the outgoing RFsignal in a delay buffer for a period of time, the time period based onthe echo signal and determined by detecting a time-delayed,cross-polarized test code signal using at least one of correlation andmatched filter techniques in the FFT domain, the test code signal beinga known test code signal.
 16. The method as set forth in claim 15,wherein a ground plane is disposed between the first antenna array andthe second antenna array to thereby provide isolation between the firstand second antenna arrays.
 17. The method as set forth in claim 15,further comprising the step of: detecting the echo signal in thedown-converted signal.
 18. The method as set forth in claim 17, furthercomprising the step of: suppressing at least a part of the echo signalfrom the down-converted signal.
 19. The method as set forth in claim 18,further comprising the step of: adding the known test signal to theoutgoing RF signal.
 20. The method as set forth in claim 19, furthercomprising the step of: detecting an echo of the test signal in thedown-converted signal; and using a delay associated with the test signalecho to determine the delay time period associated with the delaybuffer.